1. Field of the Invention
This invention relates to a deposited film forming process and a deposited film forming apparatus. More particularly, it relates to a deposited film forming process and a deposited film forming apparatus which are suited for stably forming light-receiving members having a sensitivity to electromagnetic waves such as light (which herein refers to light in a broad sense and indicates ultraviolet rays, visible rays, infrared rays, X-rays, xcex3-rays, etc.).
2. Related Background Art
Materials that form photoconductive layers in solid-state image pick-up devices or in electrophotographic light-receiving members in the field of image formation or in character readers are required to have properties as follows: They are highly sensitive, have a high SN ratio (photocurrent (Ip)/(Id)), have absorption spectra suited to spectral characteristics of electromagnetic waves to be radiated, have a high response to light, have the desired dark resistance and are harmless to human bodies when used; and also, in the solid-state image pick-up devices, the materials are required to have properties that enable easy erasure of the lag in a prescribed time. In particular, in the case of light-receiving members of electrophotographic apparatus used as business machines in offices, the harmlessness in their use is important.
Materials that attract notice from such viewpoints include amorphous silicon (hereinafter xe2x80x9ca-Si) whose dangling bonds have been modified with monovalent elements such as hydrogen or halogen atoms, and its application to electrophotographic light-receiving members is disclosed in, e.g., Japanese Patent Application Laid-Open No. 54-86341.
Electrophotographic light-receiving members are known to have various forms. Those having the form of what is called a drum are commonly used. In this case, the desired layers such as photoconductive layers, i.e., light-receiving layers are formed on the surfaces of cylindrical substrates to form light-receiving members.
When light-receiving layers comprised of a-Si are formed on cylindrical substrates, many processes are known in the art, as exemplified by sputtering, a process in which material gases are decomposed by heat (thermal CVD), a process in which material gases are decomposed by light (photo-assisted CVD) and a process in which material gases are decomposed by plasma (plasma-assisted CVD). In particular, one having been put into practical use in a very advanced state is plasma CVD (chemical vapor deposition), i.e., a process in which material gases are decomposed by direct-current or high-frequency or microwave glow discharging to form deposited films on the cylindrical substrate.
FIG. 1 is a cross-sectional schematic view showing an example of a plasma CVD system. In FIG. 1, reference numeral 6100 denotes the whole of a vacuum reactor; 6111 a cathode electrode serving also as the sidewall of the vacuum reactor; 6123 a gate that forms the top wall of the vacuum reactor; and 6121 the bottom wall of the vacuum reactor. The cathode electrode 6111 the top wall 6123 and the bottom wall 6121 are each insulated with an insulator 6122 Reference numeral 6112 denotes a cylindrical, film-forming substrate (herein meant to be a target substrate on which the deposited film is to be formed) set on an auxiliary substrate 6113-a made of a metal such as aluminum, and disposed in the vacuum reactor. The film-forming substrate 6112 is fitted with an auxiliary-substrate cap 6113-b at the top end thereof. The film-forming substrate 6112 is grounded to serve as the anode electrode. In the auxiliary substrate 6113-a, a substrate heater 6114 is disposed so as to be used to maintain the film-forming substrate at a prescribed temperature during film formation or to anneal the film-forming substrate after film formation.
Reference numeral 6115 denotes a deposited film forming material gas feed pipe, and is provided with a large number of gas release holes (not shown) through which material gases are released into the vacuum reaction space. At the other end of the material gas feed pipe 6115, the pipe communicates with a deposited film forming material gas feed system 6200 via a gas feed pipe 6117 and a valve 6260.
Reference numeral 6124 is an exhaust pipe through which the inside of the vacuum reactor is evacuated, and communicates with a vacuum exhaust system (not shown) via an exhaust valve 6119. A vacuum gauge 6120 is connected to the exhaust pipe 6124, and a reactor leak valve 6118 used when, e.g., the inside of the vacuum reactor is set open to the atmosphere is also connected to the exhaust pipe 6124. Reference numeral 6111 denotes a means for applying electric power to the cathode electrode 6111.
The deposited film forming material gas feed system 6200 has material gas cylinders 6221 to 6226 holding the desired material gases. The gas cylinders 6221 to 6226 are connected to their piping via valves 6231 to 6236 so that material gases can be flowed into mass flow controllers 6211 to 6216 via flow-in valves 6241 to 6146, respectively. From the mass flow controllers 6211 to 6216, the piping is so connected as to come to meet in the valve 6240 via flow-out valves 6251 to 6256. Pressure controllers 6261 to 6266 are connected between the material gas cylinders 6221 to 6226 and the flow-in valves 6241 to 6146, respectively, in the piping.
Such a deposited film forming apparatus employing plasma CVD is operated in the following way.
The inside of the vacuum reactor is evacuated through the exhaust pipe 6124, and also the film-forming substrate 6112 is heated to and kept at a prescribed temperature by means of the heater 6114. Next, through the material gas feed pipe 6115, when, e.g., a-Si deposited films are formed, material gases such as silane are introduced into the vacuum reactor. The material gases are released from the material gas release holes (not shown) of the gas feed pipe into the vacuum reactor. Concurrently therewith, from a voltage applying means 6116, for example a high frequency power is applied across the cathode electrode 6111 and the film-forming substrate (anode electrode) 6112 to cause plasma discharge to take place. Thus, the material gas inside the vacuum reactor is excited into excited species, where radical particles, electrons and ionic particles of Si* and SiH* (the mark * indicates an excited state) are produced and a deposited film is formed on the film-forming substrate surface by chemical mutual action between these particles themselves or between these particles and the film-forming substrate surface.
In such an instance where an electrophotographic light-receiving member comprised of, e.g., a-Si, an auxiliary substrate is inserted into the film-forming cylindrical substrate because the film-forming cylindrical substrate must be transported into the vacuum reactor and held there. Such an auxiliary substrate is also commonly inserted into the film-forming cylindrical substrate because, as disclosed in, e.g., Japanese Patent Application Laid-Open No. 60-86276, auxiliary substrates must be provided at the upper and lower part of a film-forming substrate so that its characteristics can be made uniform. Still also, e.g., Japanese Patent Application Laid-Open No. 7-181700 discloses a technique in which, for the purpose of preventing faulty images, achieving an improvement in electrophotographic performance and obtaining much uniform and high-quality images, the auxiliary substrate is basically so constituted that a material having a great thermal conductivity is used at its part facing the film-forming substrate and a material having a small coefficient of thermal expansion and a small thermal conductivity is used at the upper part and/or lower part of the auxiliary substrate.
As another example, Japanese Patent Application Laid-Open No. 7-230178 discloses a technique in which, for the purpose of preventing faulty images, achieving an improvement in electrophotographic performance and obtaining much uniform and high-quality images, the surface of an auxiliary substrate is formed of a ceramic material.
These techniques have brought about an improvement in uniformity of film thickness and film quality of electrophotographic light-receiving members and have concurrently brought about an improvement in yield, too.
Light-receiving members produced using such an apparatus have been made to have uniform film thickness and film quality and improved in yield. Under existing circumstances, however, there is room for further improvement in order to achieve an improvement of overall performances. In particular, electrophotographic apparatus are rapidly being made higher in image quality, higher in process speed and higher in durability. Accordingly, when such light-receiving members are used as electrophotographic photosensitive members, it is sought to more improve their electrical properties and photoconductive properties and also to make their performances greatly durable in every environment while maintaining charging performance and sensitivity.
Then, as a result of the achievement of improvements of optical exposure assemblies, developing assemblies, transfer assemblies and so forth in electrophotographic apparatus, having been made in order to improve image characteristics of electrophotographic apparatus, the electrophotographic photosensitive members have become sought to be much more improved in image characteristics than ever.
Under such circumstances, in respect of such subjects, the above prior art has made it possible to uniform the film thickness and film quality to a certain extent, but there is still room for improvement to achieve further improvement in image quality. In particular, as a subject for making amorphous silicon type photosensitive members (light-receiving members) achieve a much higher image quality, it is noted to obtain uniform films and also to prevent any minute faulty images from occurring. As to the minute faulty images, any films having deposited on the part other than the film-forming substrate during film formation, i.e., the inside of a reaction space and the outer surface of the auxiliary substrate, may come off and scatter on the film-forming substrate to cause abnormal growth of the deposited film. This causes occurrence of the minute faulty images when images are formed using such a substrate. Hence, any deposits of films on the part other than the film-forming substrate must be prevented from coming off and scattering on the film-forming substrate.
Accordingly, an object of the present invention is to solve the problems the prior art has had, and to provide a deposited film forming process and a deposited film forming apparatus by which any deposits of films on the part other than the film-forming substrate can be prevented from coming off and scattering on the film-forming substrate so that deposited films having uniform film thickness and film quality can steadily be formed and also faulty images can be made greatly less occur.
Another object of the present invention is to provide a deposited film forming process and a deposited film forming apparatus which can achieve improvements of various properties of films formed, deposited film forming rate, reproducibility, and productivity of films so that the yield can dramatically be improved when mass production is made.
The deposited film forming process of the present invention comprises forming a deposited film on a film-forming substrate by reduced-pressure vapor phase growth; the film-forming substrate being set on an auxiliary substrate and provided with an auxiliary-substrate cap at the upper part thereof; wherein;
a maximum temperature difference between temperature at the upper end of the film-forming substrate and temperature at the lower end of the auxiliary-substrate cap provided on the film-forming substrate at its upper part is so controlled as to be not greater than a prescribed value so that a film deposited on the auxiliary-substrate cap is improved in adhesion.
The deposited film forming apparatus of the present invention comprises a means for forming a deposited film on a film-forming substrate by reduced-pressure vapor phase growth; the film-forming substrate being set on an auxiliary substrate and provided with an auxiliary-substrate cap at the upper part thereof; wherein;
the auxiliary-substrate cap is provided with a means for preventing the surface temperature thereof from dropping that is attributable to radiation heat conducted from a substrate heating means, so as to make small a maximum temperature difference between temperature at the upper end of the film-forming substrate and temperature at the lower end of the auxiliary-substrate cap.
In these deposited film forming process and apparatus of the present invention, the deposited film may be a deposited film which forms a light-receiving member comprising an amorphous material mainly composed of silicon atoms.
In these deposited film forming process and apparatus of the present invention, the maximum temperature difference may be 15% or less, and preferably 10% or less, of the film-forming substrate temperature.
In these deposited film forming process and apparatus of the present invention, the maximum temperature difference may be a maximum temperature difference between temperature at the upper end of the film-forming substrate at its part within 20 mm from the upper end and temperature at the lower end of the auxiliary-substrate cap at its part within 20 mm from the lower end.
In these deposited film forming process and apparatus of the present invention, the auxiliary-substrate cap may have an outer surface having a surface roughness Rz of 40 xcexcm or less, and preferably 30 xcexcm or less.
In these deposited film forming process and apparatus of the present invention, the auxiliary substrate and the auxiliary-substrate cap may each be comprised basically of a metal of the same type as that of the film-forming substrate.
In these deposited film forming process and apparatus of the present invention, the auxiliary substrate and the auxiliary-substrate cap may each be comprised basically of a metal comprising aluminum.